When I think of coffee in the summer, I think of iced coffee melting in my cup as I race against time to gulp it down before it gets too warm. Iced coffee tastes wonderful — milky coffee at room temperature, less so.

I recently found another, better way of consuming iced coffee when I had a caffeine awakening in Mexico City. There, I was introduced to an espresso tónico, an espresso shot mixed with bubbly sweet tonic water. It was the only caffeinated beverage I could stand to drink in the sweaty heat under the sun. No added sugar was needed — the sugar in the quinine-laced tonic water was sweet enough without it. The tonic water could even fool me into thinking I was hydrating myself, and even after the ice of my coffee tonic melted, the carbonated and caffeinated drink still tasted refreshing.

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Coffee experts recommend sweet, floral, citrus-forward coffees.

Unlike milky lattes that require gadgets to make, preparing a coffee tonic is more accessible. I cannot froth milk to save my life, but I can reliably open and pour tonic water into my coffee. Upon my return from vacation, I began to make espresso tonics. I would pour a double espresso shot into my ice-filled cup and then add different flavors of Q Tonic on top.Surprisingly, the grapefruit and ginger beer flavors were highlights for me. I was smug with the knowledge that my fruity coffee soda looked cool and took little time to make.

Little did I know, I had joined an alliance of coffee tonic lovers. Versions of coffee tonics appeared at the Sweden-based coffee roaster Koppi in 2007, and they were popularized in several specialty coffee shops in the U.S. by 2015.

I’m here to bring that trend back. With only two necessary ingredients and plenty of room for experimentation, this is a foolproof summer drink you can enjoy at work or on the beach.

How To Properly Make An Espresso Tonic

“Your creation is only as good as the ingredients that are in it, but especially in something so simple like this,” said Emily Rosenberg, senior educator and curriculum manager of Stumptown Coffee Roasters in New York City. “You have to have high-quality tonic and high-quality coffee that’s prepared well, or there’s nothing to hide behind.”

Tonic preferences depend on who you ask. Blue Bottle uses Q Tonic, while Partners Coffee uses Boylan Heritage Tonic because it’s “not overly sweet and pairs nicely with our coffee,” according to Allie Caran, Partners’ director of education. Fever-Tree Tonic is a go-to for Stumptown, Rosenberg said. The point is to find whatever high-quality tonic laced with quinine is available near you. Quinine is key if you want a sweet, tangy flavor: The one time I tried it with regular Dasani sparkling water, the resulting drink was too sad, flat and bitter for me to enjoy.

Now the other key ingredient: coffee. At a Partners Coffee location in New York City, Caran showed me how a specialty coffee roaster is used to make a coffee tonic, which is served seasonally there. For an espresso tonic, Caran used the Bedford blend, which has tasting notes of marmalade, pomegranate and brown sugar, but she encouraged makers to experiment. “Coffee that has tasting notes that are in the fruity world, or the sweet world, or the juicy world — those are the coffees that do best in tonic,” she said.

If you’re using an espresso machine, you can do it with 18 grams of ground coffee. You pull the shot for about 28-30 seconds and should look for an output of 32-36 grams of liquid espresso, Caran said.

In her demonstration, Caran first added tonic water halfway up the cup. “If you stick to the halfway-filled mark, you shouldn’t have any overflowing happening,” she said. For the last steps, she added ice almost to the brim and then slowly added the espresso shot on top.

“I think visually, people really like the espresso floating,” Caran said. “Pouring slow is generally the best advice I can give.”

The Order In Which You Pour Ingredients Can Make A Difference

The order of ingredients does matter — to a point. Pouring the blended coffee tonic over ice versus pouring the espresso slowly on top of the ice-filled tonic did not dramatically change the flavor when I made it. But pouring espresso right into tonic did.

If you add the espresso straight into tonic water, it creates a bubbly reaction that can turn the drink into more foam than drink. “When we poured the espresso right on top of the tonic, it created a milkshake foam on top,” Caran said. “It’s not as refreshing, it’s not as cold and it’s not as balanced.”

Rosenberg recommended doing ice, tonic and then espresso as the last step. “If you put the espresso in first, first of all, you’re going to melt some of the ice, and it also makes the tonic foam up quite a bit,” she said. “Adding the ice as the last item, you’re bound to then agitate the liquid that’s already in there, which is going to increase that frothing effect.”

How To Make A Coffee Tonic With Cold Brew

If you don’t have access to an espresso maker, you can still make this drink with cold brew. When I made it at home with cold brew concentrate and Fever-Tree Indian Tonic Water I bought at a bodega, it was even quicker to make since all the ingredients were prepackaged, cold and ready to pour.

Personally, I found that espresso tonics provide more intense flavor than cold brew tonics. My nose may be the reason for that added aromatic element. “Having that coffee aroma hit your nose in the way it would with espresso may increase your perception of its intensity,” Rosenberg said.

To be clear, though, both versions are delicious. Selina Viguera, a Blue Bottle manager in Venice, California, said her location serves a cold brew tonic with Q Tonic and its Three Africas blend. “This drink is so easy for us to mix together,” she said.

She recommended a floral, citrusy-flavored cold brew to pair with the citrusy quinine flavor. “Usually, these more floral coffees highlight what’s in the tonic, or even highlight what you want to experience out of a summer drink,” she said. “You want something that’s light and will quench your thirst when it’s hot.”

For a standard 12-ounce cup, Viguera uses 150 grams of the Q Tonic — so the tonic still dominates — and 100 grams of the cold brew with Blue Bottle’s Three Africas blend.

To avoid a bubbly, foamy mess, you could also combine the cold brew on top of the tonic slowly in a measuring glass to let it settle down and then pour that mixture over the ice. “It keeps it pretty tame that way,” Viguera said.

“When you’re dealing with espresso, which is typically an ounce to two ounces, you can play around with more tonic because it will hold the bite longer versus when you’re using cold brew, you need a good amount of it to taste the coffee,” she said. That’s why she suggests not diluting your cold brew at home and finding a tonic that has a good bite to it, like Q Tonic.

At Partners, Caran first poured the tonic, let it settle and then topped with ice. The ice acts as a barrier against more fizziness when the cold brew is poured. Stir together and sip at your leisure. Ahhh.